There are many terms for the head of a local church, and the exact differences blur over time. Often the choice is based on some theological position of the founder; a distinction that is often lost in the general homogenization of ecumenicalism.
Nonetheless, in terms of a theological position, a vicar is someone who stands in place of Christ. A person who represents Christ, the real head of the church, at the church. He has a special spiritual position and role.
A pastor is specifically someone concerned with pastoral work, that is someone who heals the wounds and broken hearts. This is frequently used in churches where the leader doesn't necessarily have a special spiritual position, he is a teaching elder, or just a selected congregant. In the UK and outside the US this person is often called a minister, which has essentially the same meaning.
A priest is much the same as a vicar, except that a priest often has the role of offering a sacrifice, which is why you see it in Catholic churches, which offer the Eucharist, the re-sacrifice of the body of Christ.
These names are often reflected in the three basic categories of church:
Episcopal, which is a church with a hierarchy of spiritual leadership such as the Church of England or the Roman Catholic church. They usually use either priest, or vicar. (And also various higher level titles like Bishop, Cardinal, Monseigneur etc.) The name derives from the Greek work episcopos, which literally means overseer, or, more conventionally bishop.
Presbyterian, which is a church ruled by elders with a central congregation of elders from each church that, democratically, set church doctrine. Examples of this would be the Baptists, the Church of Scotland, or the Methodists. They tend to use words like pastor, minister or often just elder or teaching elder. This name derives from the Greek word presbyter meaning elder, the literal meaning being that everyone is the same but the wiser older ones set the standards.
Congregational, which is largely like the Presbyterian, except that there is not ruling body of doctrine set by the churches as a group. Each church is responsible for its own. There are lots of little churches like this, and some larger ones. They often have an overall organization, but it has limited governing powers.
The two words are pretty much synonyms in all contexts, but if a distinction can ever be made, perhaps leafage sometimes alludes slightly more to the individual leaves (albeit, collectively). I don't advance this possibility particularly strongly, because I don't think I really believe it myself.
Thus you might see leafage pattern used relatively more often to refer to the "average" pattern on each leaf, as opposed to the foliage pattern referring to the overall disposition of leaves on the plant. By "relatively" there, I mean after allowing for the fact that "foliage" is much more common in the first place.
The general advice would simply be; forget about using the word "leafage". There are no contexts where "foliage" would actually be wrong, and using the uncommon word may stand out as "odd".
Best Answer
Cooperating means working with someone in the sense of enabling: making them more able to do something (typically by providing information or resources they wouldn't otherwise have).
Collaborating means actually working alongside someone (from Latin laborare: to work) to achieve something.
The confusion comes from the overloaded meaning of "work with": In the "Work with me, people" sense, it means to go along with my idea - it's a passive condoning or suspension of disbelief rather than an active involvement. In the "I'm stuck, can you work with me on this problem?" sense it is a request for active commitment.
So in terms of helping achieve something, the ordering is something like collaboration, then cooperation, then passive indifference, then active obstruction.