Small firm in tall building (5)
I believe the answer is:
shard
'tall building' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'small firm' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'firm' becomes 'hard' (both can mean durable or strong).
's'+'hard'='SHARD'
'in' is the link.
Can you help me to learn more?
(Other definitions for shard that I've seen before include "Bit of pottery" , "Sharp glass fragment" , "Sharp piece of glass" , "archaeological find" , "Go well with; attire" .)