Refuse a new entry — getting tense within just a short distance (9)
I believe the answer is:
nanometre
'short distance' is the definition.
(I've seen this before)
'refuse a new entry getting tense within' is the wordplay.
'refuse' becomes 'no'.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'entry' indicates putting letters inside.
'getting tense within' becomes 'metre' (I can't justify this - if you can you should give a lot more credence to this answer).
'a'+'n'='an'
'no' placed around 'an' is 'nano'.
'nano'+'metre'='NANOMETRE'
'just a' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for nanometre that I've seen before include "tiny distance" , "Some tiny measure" , "short distance" , "Very, very short length" , "small unit" .)