Origin of the word
The noun diligence is from the middle of the 14th century, and the adjective diligent dates from the same time. Both adjective and noun originate from Old French ‘diligent’ and ‘diligence’, respectively; the noun meaning ‘care and attention’ and also ‘speed or haste’. The Latin adjective was ‘diligens’, in the accusative form ‘diligentem’, and the noun was ‘diligentia’, meaning ‘carefulness, attentiveness’. Interestingly, the Latin verb ‘diligere’ had the additional sense of ‘value highly, prize, love’.
The modern word diligent gradually evolved via all these meanings, thus from ‘love’ through ‘paying attention’ to ‘being careful’ and ‘making a steady effort’ (1).
The secondary meaning of the Old French ‘diligence’ as ‘speed or haste’ took on another role in the French phrase ‘carrosse de diligence’, which came into English in the late 17th century as diligence meaning a ‘public stagecoach’, a large horse-drawn vehicle used to carry passengers and mail.
Related words: diligently
Undertaking a diligent search requires the searcher to work hard and take great care:
“Orphan works are copyright works where one or more right holder is unknown or cannot be located. These guides will be helpful if you decide to apply for a licence under the orphan works licensing scheme, which requires a diligent search to be completed. They include details on the sources that applicants must consult and a non exhaustive list of additional sources which might be helpful… Checklists to show that you have completed a diligent search have also been published, which may be used in the application process.” H.M. Government. Updated 30 September 2016: Intellectual Property Office ‘Orphan works diligent search guidance for applicants’ (1).
In the days before travel by plane, car or train, the ‘carrosse de diligence’ was a popular means of transport for the general public:
“Once having reached an English port, the aim of all travellers was to leave it as soon as possible. There were several means available. English people of the upper classes generally travelled in their carriages, drawn by their own horses, or when posting had been established, by post horses… The stage-coach was certainly cheaper. The charge was 2d. or 3d. a mile with tips at the end of the journey to guard and coachman. In his own country, the foreign traveller had been accustomed to the stage-coach or diligence and it was by this means that he usually journeyed to his destination.” Rosamund Blayne-Powell. 1951: Travellers in 18th Century England.
1. someone who is diligent works very hard and very carefully