Kautilya's Arthashastra 6.2.16

6.2.16

arisampadyuktaḥ sāmantaḥ śatruḥ, vyasanī yātavyaḥ, anapāśrayo durbalāśrayo vocchedanīyaḥ, viparyaye pīḍanīyaḥ karśanīyo vā //

A neighbouring foe of considerable power is styled an enemy; and when he is involved in calamities or has taken himself to evil ways, he becomes assailable; and when he has little or no help, he becomes destructible; otherwise (i.e., when he is provided with some help), he deserves to be harassed or reduced. Such are the aspects of an enemy.