The opposite of 'big' is little.
It could be either taller (height) or longer(length).
The word small (meaning little) is the opposite of large (meaning big).
The 5 letter word small is the opposite of big.
Small, tiny, little, minuscule.
Little
The opposite of unusual is common.
sooner
mighty
This question in unanswered.
"prompt" is one possibility
a six letter word meaning not attractive: SO UGLY!
A six letter word that has the same meaning of 'rue' is regret.
Sudden
little
reward
export
client