#!/bin/bash
var="one two three four giberish-giberish five giberish-giberish six"
sed -E 's/\s*\S{7,}//g' <<< "$var"
perl -pe 's/\s*\S{7,}//g' <<< "$var"
sed 's~[[:space:]]*[^[:space:]]\{7,\}~~g' <<< "$var"