clench
verb (used with object)
to close (the hands, teeth, etc.) tightly.
Used to describe an action that began in the past, has continued continuously, and is still in progress.
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Jones has been clenching those eyes tighter lately.
From Forbes ● Nov. 17, 2013