Double consonance is a form of near rhyme in which the stressed syllables share the same opening and closing consonant sounds, but the vowel sound changes. Words like groan and green show the pattern: the consonants frame the vowel, yet the match is incomplete, so the sound feels linked without fully rhyming.
Poets use double consonance to create echo, tension, or an unsettled musical effect. It is closely related to pararhyme, and the two terms are often used for the same device.
Example
The wind came down the hill to moan,
then touched the grass and turned to green,
a faint near-rhyme between the stone
and all the living air between.