From MELLO, M.C. - Law Dictionary, pages 436 and 463.

this refers to the person whose life is insured and I see it often.
Policyholder is still the best term for tomador de seguro - because the policyholder may not be the one whose life is insured.

É o que diz o meu "Elsevier's Dictionary of Insurance and Risk Prevention", em cinco idiomas.

Preneur d'assurance, em francês;
Tomador de seguro, em espanhol;
Versicherungsnehmer (VN), em alemão.

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Note added at 33 mins (2007-11-08 21:03:07 GMT)
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Veja as estatísticas no Google:

24,500 English pages for "insuring party".
19,700 English pages for "insurance party".
263 English pages for "insurance taker".

Alguns exemplos:

InsuranceInsurance is a contract, known as a ``policy,'' in which the insuring party is bound to perform a specified action or set thereof which materially benefits ...
www.mega.nu:8080/webconst/section_Insurance.html

SEC Info - Futon World Inc - 10SB12G/A - On 6/18/99 - EX-10.2As used in this Paragraph 8, the term "insuring party" shall mean the party who has the ... The insuring party shall be designated in Paragraph 46 hereof. ...
www.secinfo.com/dV3p8.6Bc.9.htm


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Note added at 2 hrs (2007-11-08 23:27:27 GMT)
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This text is from the second example:

Insuring Party. As used in this Paragraph 8, the term "insuring party" shall mean the party who has the obligation to obtain the Property insurance required hereunder. The insuring party shall be designated in Paragraph 46 hereof. In the event Lessor is the insuring party, Lessor shall also maintain the liability insurance described in paragraph 8.2 hereof, in addition to, and not in lieu of, the insurance required to be maintained by Lessee under said
paragraph 8.2, but Lessor shall not be required to name Lessee as an additional insured on such policy. Whether the insuring party is the Lessor or the Lessee, Lessee shall, as additional rent for the Premises, pay the cost of all insurance required hereunder, except for that portion of the cost attributable to Lessor's liability insurance coverage in excess of $1,000,000 per occurrence. If Lessor is the insuring party Lessee shall, within ten (10) days following demand by Lessor, reimburse Lessor for the cost of the insurance so obtained.