• 互角ごかく — evenly matched; equal
• 相互そうご — mutual; reciprocal
• 交互こうご — alternately; by turns
• 互換性ごかんせい — compatibility; interchangeability
• 互恵ごけい — mutual benefit; reciprocity
• 互助ごじょ — mutual aid; helping each other
• 互たがいに — each other; one another
• 互たがい違ちがい — alternation; zigzag arrangement

互 shows a design of lines intertwining like two parts crossing — originally tools entwined together. By extension, it came to mean mutual, reciprocal, or shared.