Stare endlessly into space (3)
I believe the answer is:
gap
'space' is the definition.
(gap is a kind of space)
'stare endlessly' is the wordplay.
'stare' becomes 'gape' (gape is a kind of stare).
'endlessly' means to remove the last letter.
'gape' with its last letter taken off is 'GAP'.
'into' is the link.
(Other definitions for gap that I've seen before include "prospective students may enjoy this year?" , "Hiatus" , "A break or opening as in a hedge" , "Small opening" , "Vacancy" .)