From Longman Dictionary of Contemporary Englishunderneathun‧der‧neath1 /ˌʌndəˈniːθ $ -ər-/ ●●● S2 preposition, adverb 1 UNDER/BELOWdirectly under another object or covered by it He got out of the car and looked underneath. It’s near where the railway goes underneath the road. She was wearing a smart jacket with a T-shirt underneath. Her blonde hair was hidden underneath a baseball cap.► see thesaurus at under2 on the lower surface of something The car was rusty underneath. A number had been painted underneath the table.3 CHARACTER/PERSONALITYused to say what someone’s character is really like when their behaviour shows a different character She seems confident, but she’s really quite shy underneath. I think he’s a genuinely nice guy underneath it all.
Examples from the Corpus
underneath• There's a picture with a short article underneath.• She seems aggressive, but underneath she's pretty shy.• The stream actually runs underneath the building.underneath it all• But they are very fond of him, underneath it all.• He knew he was a Republican, underneath it all, and Mallachy flattered that.• He likes to show people his tough side, but underneath it all, he's a decent person.• He seems different, but underneath it all he's the same as the rest of them.• Because underneath it all she was as strong as him and that strength appealed to him, making her a challenge.• And underneath it all was a sour feeling that at any minute the very pillars of life could collapse.underneathunderneath2 noun British English → the underneathExamples from the Corpus
underneath• The trees therefore have the characteristic that you can see under them - the underneath of an oak is almost perfectly level.Origin underneath Old English underneothan, from under + neothan “below” 