Put your oar in

‘Put your oar in’ derives from an earlier variant of the phrase ‘put (or have) an oar in another man’s boat’. This earlier form was coined in the Tudor period and was quite a commonplace saying then.

It is a reasonable hypothesis that the expression was a form of Tudor innuendo. We can suppose that ‘another’s man’s boat’ referred to his wife. I’ll leave what the oar might have alluded to to your imagination.

The first person known to have put the phrase into print was the industrious scholar Nicholas Udall in his translation of Apophthegmes of Erasmus in 1542:

In eche mannes bote, would he haue an ore,
But no woorde, to good purpose, lesse or more.

The migration to ‘put/stick your oar in’ took place over some centuries. The ‘oar in another man’s boat’ form continued to be used into the 18th century.