Grand daughter had dinner inside, unable to leave the building (5)
I believe the answer is:
gated
'unable to leave the building' is the definition.
I can't judge whether this definition defines the answer.
'grand daughter had dinner inside' is the wordplay.
'grand' becomes 'g' (G is short for grand as in a thousand).
'daughter' becomes 'd' (genealogical abbreviation).
'had dinner' becomes 'ate' (I've seen this in another clue).
'inside' means one lot of letters goes inside another.
'g'+'d'='gd'
'gd' going around 'ate' is 'GATED'.
Can you help me to learn more?
(Other definitions for gated that I've seen before include "Confined to college" , "deprived of liberty for a while" , "Kept in as punishment" , "temporarily confined" , "Under curfew" .)