Definition of ply verb from the Oxford Advanced Learner's Dictionary

ply

verb
plaɪ
 
; plaɪ
 
 
plies, plying, plied, plied1 [intransitive, transitive] (literary or Indian English) (of ships, buses, etc.) to travel regularly along a particular route or between two particular places+ adverb/preposition Ferries ply across a narrow strait to the island.The train plies twice a day between Paris and Madrid.Buses ply regularly to and from these places.ply something canals plied by gondolas and steam boatsships plying the route between Tripoli and Malta2 [transitive] ply something (formal) to use a tool, especially in a skilful wayThe tailor delicately plied his needle.
Idioms

ply your trade

to do your work or business
This is the restaurant where he plied his trade as a cook.Drug dealers openly plied their trade in front of children.

ply for hire/trade/business

(British English) to look for customers, passengers, etc. in order to do businesstaxis plying for hire outside the theatre
Phrasal verbs

ply somebody with something

1 to keep giving somebody large amounts of something, especially food and/or drinkShe plied us with tea and cake.2 to keep asking somebody questionsHe plied me with questions from the moment he arrived.