friendly

1. (in compounds) Compatible with, or not damaging to (the compounded noun).Examples: "The cobbled streets aren't very bike-friendly."; "Organic farms only use soil-friendly fertilisers."; "Our sandwiches are made with dolphin-friendly tuna."in-compounds

2. (usually military) Of or pertaining to friendlies (friendly noun sense 2, below). Also applied to other bipolar confrontations, such as team sports.Examples: "The soldier was killed by friendly fire."; "It is clear that the firing of very heavy guns, or the enemy's fire in return, would very seriously interfere with an abbatis, or anything of that kind, and it will only be something of the lightest character, or something that is placed at a considerable distance from the friendly fire, the fire of the gun itself, that would remain."; "The slaughter of one's own troops by being fired into by their friends in rear. We are very much concerned over the question of avoiding loss from the enemy's bullets while passing through the danger zone, but what have we done to avoid our bravest fellows, the survival of the fittest, those who have gotten to the front and have held on to hard-won positions—what have we done to avoid their being shot to pieces by friendly fire? Absolutely nothing that we have ever heard of—and yet this is one of the most serious problems that confronts the leader of troops. Courage before the enemy will quail before a fire from the rear."usually

3. (number theory) Being or relating to two or more natural numbers with a common abundancy.Examples: "friendly"; "friendly pairs"; "friendly n-tuples"