Answer: underpin

AnswerCrossword Clue
UNDERPINSupport from below
UNDERPINGive support to
UNDERPINSupport
underpinto support from below
underpinto replace or strengthen the foundation of (a building or the like)
underpinto furnish a foundation for; corroborate
underpinto prop up or support from below; strengthen, as by reinforcing a foundation