Page 118 - Practical English Usage 3ed - Michael Swan, Oxford

5 'less than': under
We usually use under, not below, to mean 'less than' or 'younger than'. There were under twenty people at the lecture.
You can't see this film ifyou're under 18.
6 underneath
Underneath is sometimes used as a preposition instead of under, but only for physical position. Compare:
There's a mouse under(neath) the piano. He's still under 18. (NOT ••• r:tnderttettth 18.)
7 beneath
Beneath is used mostly in a rather literary style. The ship sank slowly beneath the waves.
It is common before abstract nouns in some fixed expressions.
He acts as if1 was beneath his notice. (= not worth considering) Her behaviour is beneath contempt. (= really disgraceful)
8 adverbs
Below can be used as an adverb.
We looked over the cliffat the waves crashing on the rocks below.
Under can be used as an adverb particle (see 20) with some verbs. A lot o f businesses are going under because o f the economic crisis.
In other cases we prefer underneath for adverbial use.
1 can't take my sweater off-1 haven't got anything on underneath.
(NOT ••• tJllythirtg I'm ltlrder;)
In a book or a paper, see below means 'look at something written later'.
The difference between above and over is similar to the difference between below and under. See 6 for details.
101 beside and besides
Beside is a preposition meaning 'at the side of, 'by', 'next to'. Who's the big guy sitting beside Jane?
Besides can be used like as well as (see 78), when we add new information to what is already known.
Besides literature, we have to study history and philosophy.
Who was at the party besides Jack and the Bensons?
Besides can also be used as a discourse marker (see 157.11) meaning 'also', 'as well', 'in any case'. It is often used to add a stronger, more conclusive argument to what has gone before. In this case, besides usually goes at the beginning of a clause.
1 don't like those shoes; besides, they're too expensive. It's too late to go out now. Besides, it's starting to rain.
beside and besides 101
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