two are better than one (5)
I believe the answer is:
heads
'two are better than one' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for heads that I've seen before include "Goes for" , "Noddles; nuts" , "Coin-tossing call" , "School principals" , "a 50-50 chance" .)