Does Not Contain Definition Of enabled?

private BoxCollider Hand_L;
private BoxCollider Hand_R;

private Animator anim;
private BossHealth bossHealth;

void Awake ()
{
	anim = GetComponentInChildren<Animator> ();
	bossHealth = GetComponentInChildren<BossHealth> ();

	Hand_L = GameObject.FindGameObjectWithTag ("Hand_L").GetComponent<BoxCollider> ();
	Hand_R = GameObject.FindGameObjectWithTag ("Hand_R").GetComponent<BoxCollider> ();


}


// Update is called once per frame
void Update () {

	if (bossAwake) {
		print ("Boss is Awake");

		anim.SetBool ("bossAwake", true);

		if (inBattle) 
		{
			if (!attacking) {
				idleTimer += Time.deltaTime;
			} else {
				idleTimer = 0.0f;
				attackTimer += Time.deltaTime;
				if (attackTimer > attackWaitTime) {
					attacking = false;
					attackTimer = 0.0f;
					print ("Boss SMASH");

					**Hand_L.collider.enabled = true;
					Hand_R.collider.enabled = true;**
				}
			}

BoxCollider does not have a member collider. Instead of

Hand_L.collider.enabled = true;
Hand_R.collider.enabled = true;

you need to do

Hand_L.enabled = true;
Hand_R.enabled = true;