off one's tree

9.9

To behave in a very strange and unreasonable way

idiom

Offensive

: loco

I must have been off my tree to think I could finish the project in one night.

Examples

When she started talking to her plants, I realized she was definitely off her tree.
She's off her tree.

The Russia House (1990)
After that last decision, people thought he was really off his tree.

Synonyms

nutty

vsoff one's tree

Informal

55 7.2

Being a little crazy in a funny or strange way

covers the same irrational idea but can imply stronger oddness

off-the-wall

vsoff one's tree

Informal

7 8.0

Strange and often funny in a surprising way

relates specifically to irrational or eccentric behaviour rather than odd style

nutty as a fruitcake

vsoff one's tree

Informal

1 9.0

Very strange and silly in a way that seems crazy

means unreasonable or eccentric but at a more usual intensity

off one's trolley

vsoff one's tree

Offensive

1 9.9

Acting in a strange, confused way and not thinking clearly

focuses on general irrational or eccentric behaviour rather than only thoughtlessness

off one's nut

vsoff one's tree

Offensive

9.9

Acting in a very strange and not sensible way

is the informal idea of being unreasonable or eccentric

off one's box

vsoff one's tree

Archaic

9.9

Feeling confused and out of control after drinking or when very upset

covers irrational or eccentric behaviour more generally, not only temporary causes

bonkers

vsoff one's tree

Informal

8.0

Acting or feeling very strange

is the broader idea of unreasonable or eccentric conduct

off one's dot

vsoff one's tree

Archaic

9.9

Acting strange or a little crazy

signals more obvious unreasonable or eccentric conduct rather than mild oddness

Antonyms

normal

∞ 1.0

Usual or expected in most situations

sane

119 3.2

Having a healthy mind and able to think clearly

How Crazy

insane

Slur

524 4.0

off one's tree

Offensive

9.9

crazy

Slur

40 7.2

eccentric

1 7.0

odd

798 1.0

Surface Forms

off one's tree positive

Morphology

off + one's + tree

The meaning 'crazy' is idiomatic and not a predictable combination of 'off' (which can mean 'not right' or 'away from'), 'one's', and the literal noun 'tree'. A B1 learner who knows the individual words would not reliably infer this slang sense; the expression is culture-specific and requires exposure, so it is opaque.

Etymology

Off one's tree is a slang phrase that one popular story says comes from the picture of someone falling off a tree and then acting confused or wild. That's why the phrase means 'crazy' or 'not thinking clearly'.