Which is not an agency of the UNO?

A specialized agency of the United Nations is an autonomous international organisation - with its own charter, membership, budget, and governing body - that is brought into a formal working relationship with the UN under Articles 57 and 63 of the UN Charter. This is different from the UN's own principal organs, which are created directly by the UN Charter itself and function as integral parts of the UN rather than as separate agencies linked to it.

Checking each body listed against this definition:

• Food and Agriculture Organization (FAO) - founded 1945, an autonomous UN specialized agency working on global food security and agricultural development.

• United Nations Educational, Scientific and Cultural Organization (UNESCO) - founded in 1945 (its constitution entered into force in 1946), an autonomous UN specialized agency for education, science and culture.

• World Health Organization (WHO) - founded 1948, an autonomous UN specialized agency for international public health.

• International Court of Justice (ICJ) - one of the six principal organs of the UN, created directly under Chapter XIV of the UN Charter as the organisation's own judicial arm - not a separate specialized agency.

Testing each against the specialized-agency definition confirms the split: FAO, UNESCO and WHO each have their own separate membership and governing structure joined to the UN through a relationship agreement, so all three satisfy the test. The ICJ has no such separate relationship agreement - it sits inside the UN Charter itself alongside the General Assembly, Security Council, ECOSOC, Trusteeship Council and Secretariat as one of the six principal organs.

So among the four bodies listed, the International Court of Justice is the one that is not an agency of the UNO.