pace, rate, chat (slang)... Or if you mean the drug: sulf, whiz, meth.
sawn
"four-letter word" is another phrase meaning "curse word, so the phrase might mean that boobies is not a scientific word for breasts, but it's not considered vulgar, either.
Jack.
A four letter word starting with the letter a is able.
It depends on what you mean by 'four letter word'. Thea has four letters, so yes it is. It is not a swear word, so it's not that kind of 'four letter word'.
rate
knot
The word heart is another four-letter word that is related to your circulatory system.
'Cans' is another word for 'tins'.
door?
over
sawn
west?
door
thaw
loot
Mind.