"slackening" in the noun sense
1. relaxation, loosening, slackening
an occurrence of control or strength weakening
"the relaxation of requirements"
"the loosening of his grip"
"the slackening of the wind"
"slackening" in the verb sense
1. slow, slow down, slow up, slack, slacken
become slow or slower
"Production slowed"
2. slack, slacken, slack up, relax
make less active or fast
"He slackened his pace as he got tired"
"Don't relax your efforts now"
3. slacken
become looser or slack
"the rope slackened"
4. slacken, remit
make slack as by lessening tension or firmness
Source: WordNet® (An amazing lexical database of English)
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