Mētralṓias (μητραλῴας) means one who strikes or kills his mother. From mētēr (mother) + aloiaō (to strike). It appears in Paul's vice list in 1 Timothy 1.
First Timothy 1:9-10 lists those for whom the law exists: 'the lawless and rebellious... those who kill their fathers or mothers, murderers...' The list escalates from general to extreme violations. Striking a parent represented the ultimate violation of family honor and natural law. The law exposes sin in its most naked form, driving sinners to grace. Paul himself was once 'the worst of sinners' (1:15-16) and received mercy — no sin is beyond Christ's redemption.