think straight

to think clearly. (Often negative.) I'm so tired I can't think straight.

to use your mind effectively The actor said she was so surprised to be nominated for an award that she still can't think straight.

Usage notes: usually used in a negative way, as in the example

Name	Pronounced	Usage
Leonora	-	Italian
Len	LEN	English
Babs	BABS	English
Xabier	sha-bee-ER	Basque, Galician
Asha (2)	-	Eastern African, Swahili
Ron (2)	-	Hebrew