Fetching details from the dictionary...

fat; thick
deep (of a voice); thick; sonorous
daring; shameless; brazen; audacious
この木の幹はかなり太い。
The trunk of this tree is quite thick.
声が太くていい声だね。
You have a nice deep voice.
太い線でしっかり描いてね。
Draw firmly with thick lines.