boo

UK: /ˈbuː/ US: /bu/ ,(bo̅o̅; also Slang bō)

Inflections of 'boo' (n): npl: boos

Inflections of 'boo' (v): (⇒ conjugate)

boos

v 3rd person singular

booing

v pres p

booed

v past

booed

v past p

WordReference Random House Learner's Dictionary of American English © 2025

boo¹ /bu/   interj., n., pl. boos, v. 
interj. 

1. (used to express contempt or disapproval or to startle or frighten):
   "Boo! Did I scare you?'' she asked.

n. [countable]

2. an exclamation of contempt or disapproval:
   a boo from the bleachers.

v. 

3. to cry "boo'' (at someone): [no object]
   The fans booed when it became clear that their team would lose again.
   [~ + object]
   The fans booed the pitcher.

WordReference Random House Unabridged Dictionary of American English © 2025

boo¹  (bo̅o̅), interj., n., pl. boos, v., booed, boo•ing. 
interj. 

1. (used to express contempt or disapprobation or to startle or frighten).

n. 

2. an exclamation of contempt or disapproval:
   a loud boo from the bleachers.

v.i. 

3. to cry boo in derision.

v.t. 

4. to show disapproval of by booing.

• expressive formation 1810–20

boo²  (bo̅o̅, bō), n. 

1. Drugs, Slang Terms [Slang.] marijuana. Also called boo grass. 

• of uncertain origin, originally 1955–60

Collins Concise English Dictionary © HarperCollins Publishers::

boo / buː/ interjection

1. an exclamation uttered to startle or surprise someone, esp a child
2. a shout uttered to express disgust, dissatisfaction, or contempt, esp at a theatrical production, political meeting, etc

verb (boos, booing, booed)

1. to shout "boo" at (someone or something), esp as an expression of disgust, dissatisfaction, or disapproval: to boo the actors