Gaidher or Gaidhar is a word of Gujarati

Gujarati language

Gujarati is an Indo-Aryan language, and part of the greater Indo-European language family. It is derived from a language called Old Gujarati which is the ancestor language of the modern Gujarati and Rajasthani languages...

, Kutchi

Kutchi language

Kachhi Kachhi Kachhi (also spelt Cutchi, Kutchhi or Kachchhi, is an Indo-Aryan Language spoken in the Kutch region of the Indian state of Gujarat as well as in Sindh.- Closely related languages :...

 and Rajasthani language

Rajasthani language

Rajasthani Rajasthani Rajasthani (Devanagari: , Perso-Arabic: is a language of the Indo-Aryan languages family. It is spoken by 50 million people in Rajasthan and other states of India and in some areas of Pakistan. The number of speakers may be up to 80 million worldwide...

. The word Gaidher derives its origin from the word Gadh or Garh. The word Gadh in north Indian languages like Hindi

Hindi

Standard Hindi, or more precisely Modern Standard Hindi, also known as Manak Hindi , High Hindi, Nagari Hindi, and Literary Hindi, is a standardized and sanskritized register of the Hindustani language derived from the Khariboli dialect of Delhi...

, Gujarati, Rajasthani, Marwari

Marwari language

The Marwari language , also variously Marvari, Marwadi, Marvadi), is spoken in the Indian state of Rajasthan. Marwari is also found in the neighboring state of Gujarat and Haryana and in Eastern Pakistan...

, Marathi

Marathi language

Marathi is an Indo-Aryan language spoken by the Marathi people of western and central India. It is the official language of the state of Maharashtra. There are over 68 million fluent speakers worldwide. Marathi has the fourth largest number of native speakers in India and is the fifteenth most...

 means a fort, like Chittorgarh

Chittorgarh

Chittorgarh is a city and a municipality in Rajasthan state of western India. It lies on the Berach River, a tributary of the Banas, and is the administrative headquarters of Chittorgharh District and a former capital of the Sisodia clans of Rajputs of Mewar...

, Sinhgadh

Sinhagad

Sinhagad, Sinhgarh, or Sinhgad , is a fortress located roughly 30 kilometres southwest of the city of Pune, India. Previously called Kondhana , the fort has been the site of many important battles, most notably the battle of Sinhagad in 1670...

, Mehrangadh

Mehrangarh Fort

Mehrangarh Fort, located in Jodhpur city in Rajasthan state, is one of the largest forts in India.The fort is situated 400 feet above the city and is enclosed by imposing thick walls. Inside its boundaries there are several palaces known for their intricate carvings and expansive courtyards. A...

.

The persons who were expert and had skilled knowledge to plan and build a fort were called Gaidher or Gaidhar. Gaidhar literally also means a construction foreman or a Master Mason.. Forts were built at strategic locations, often on a hill-top, to guard the kingdoms. Gaidhar held a important place in king's court and were looked upon with respect.

Gaidhar were appointed by kings, upon their skills and also loyalty. Gaidher were persons of high integrity as they used to make the blue-print of fort and whole forts were erected under his supervision and guidance. The kings used to trust them and they had the power and authority to hire manual labourers and skilled masons for such construction works. For example, members from Mistri community, who were master-builders, were usually appointed as Gaidher in Princely State of Cutch.

In English

English language

English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

, tn can be defined as Chief Engineer. Usually one Gaidher was appointed by the king as Gaidher of the "Raaj" (kingdom). Sometimes upon requirement another, two or three Gaidhers were then appointed with his consultation by king and they used to work under head Gaidher as their assistants, Something like Assistant Engineer.

Surname

This is also one of the occupational surnames found in persons of India or Indian origin.
In India or persons of Indian origin you can find many people using Gaidhar or Gaidher as a surname. The persons using this surname are usually found in people of Rajasthan

Rajasthan

Rājasthān the land of Rajasthanis, , is the largest state of the Republic of India by area. It is located in the northwest of India. It encompasses most of the area of the large, inhospitable Great Indian Desert , which has an edge paralleling the Sutlej-Indus river valley along its border with...

 and Gujarat. As explained above, the descendants of persons working as Gaidher, later started using it as a surname.