Underis a preposition.When we useunderas a preposition, it is similar tobelow. We useunderto talk about something that is below or lower than something else:
The cat isunderthe table.
His shoes wereunderhis bed.
When we useunder, we can also mean that one thing is touching or covering something else. We do not usebelowin this way:
The wreck of the Titanic still remainsunderthe sea.
Not: …below the sea.
He had hidden the moneyunderthe floorboards.
Not: …below the floorboards.
We don’t useunderto refer to something in a lower position than something else. We usebelow:
Venus is justbelowthe moon right now.
Not:Venus is just under the moon…
Age
We useunder, notbelow, to refer to age:
You have to beunder18 to get an allowance.
They have three childrenunderthe age of five.
Measurements
We useunder, notbelow, to talk about measurements of time and weight:
We finished the project inundera year and a half.
The bag was justunder10 kilos, so I was able to bring it on the plane.
When we talk about height and temperature, we usebelownotunder:
The roof of the new building is justbelowthe height of the church and I think it distracts from the church.
Not: …under the height of the church…
The liquid must be keptbelowfive degrees.(preferred to… under five degrees.)
Underneathis similar tounder, but it usually only refers to position:
Underneaththe stairs is where we keep our vacuum cleaner and brushes.
The child weighedunderfive kilos.
Not: …underneath five kilos.
See also:
Below
Beneath