Ply one's trade

He worked in the trade.

Plied is the past tense of ply
http://dictionary.reference.com/search?q=ply

ply
v. plied, (pld) ply·ing, plies (plz)
v. tr.

1. To use diligently; wield: ply a knitting needle.
2. To engage in diligently; practice: plied the carpenter's trade.
3. To traverse or sail over regularly: Trading ships plied the routes between coastal ports.
4. To continue offering something to; ensure that (another) is abundantly served: plied their guests with excellent food.
5. To assail vigorously.

v. intr.

1. To traverse a route or course regularly: The boat plies between the islands on a weekly schedule.
2. To perform or work diligently or regularly: plied at the weaver's trade for 20 years.
3. Nautical. To work against the wind by a zigzag course; tack.

ALSO

ply
plied, (pld) ply·ing, plies (plz)

1. To join together, as by molding or twisting.
2. To double over (cloth, for example).

Dadpad, may I ask u a question in this way: How long have you plied (at) the linguist's trade?

G'day littlecrab.

I smiled/laughed at your post because I am not actually known at home for my linguistic skills. Not many aussies are.

Hehe, dadpad, I don't know much, but I know u r a nice Aussie. Am I right?

Thank you!
Thank you for your help!