What archaeologists may find strenuous, spades to the fore (5)
I believe the answer is:
shard
'what archaeologists may find' is the definition.
'strenuous spades to the fore' is the wordplay.
'strenuous' becomes 'hard' ('hard' can be a synonym of 'strenuous').
'spades' becomes 's' (abbreviation in card games).
'to the fore' means one lot of letters go next to another.
'hard' after 's' is 'SHARD'.
(Other definitions for shard that I've seen before include "Bit of pottery" , "archaeological find" , "Broken piece of a brittle artefact" , "remnant after break-up" , "construction in London" .)