Get the measure of plumbers (6)
I believe the answer is:
fathom
'get' is the definition.
(thesaurus)
'the measure of plumbers' is the wordplay.
I cannot quite see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'measure' could be 'm' (m is a kind of measure) and 'm' is present in the answer.
'of' could be 'o' and 'o' is located in the answer.
The remaining letters 'fah' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for fathom that I've seen before include "Come to understand - unit of depth" , "Measure of depth, 6 ft." , "Measure of marine depth" , "It's six feet deep" , "Six feet in depth; grasp" .)