Keen nooc ka mid ah weedhan adag ee kiimikada, esters waa xeryo kiimiko ah oo laga soo saaro iskudhafka aashitada iyo aalkolada.
Dabcan, nooc ka mid ah jumlada ayaa ah "Kiimiko ahaan, esters waa xeryahooda kiimikada oo laga soo qaatay aashitada aan dabiiciga ahayn ama aashitada dabiiciga ah ee ugu yaraan hal - OH (hydroxyl) koox lagu beddelay koox - O - alkyl (alkoxy) ah. "